PENNSYLVANIA AND DEPOSITS THEREIN. 51 



Delaware and Allegheny rivers. Of the character of his work no 

 encomium is necessary. 



Storm King Mountain Ponding. 



The Cambro-Ordovician rock floor of the Champlain-Hudson 

 trough varies slightly on either side of the meridian until it ap- 

 proaches Kingston, N. Y., where it forks. The right-hand fork 

 turns westward along a deflection of 20 degrees into the Cambro- 

 Ordovician trough of the Rondout-Wallkill Valley, which is sepa- 

 rated from a short valley in the same measures, leading to Delaware 

 River, by a low saddle at 514 feet. Across this stream the Great 

 Valley of Pennsylvania extends, in the same measures, to Maryland, 

 with the highest point of its trough slightly below 500 feet. The 

 left branch turns, at the same angle, eastward into a pocket through 

 which Hudson River flows. The high eastern wall of this valley 

 leaves its average of 16 miles from the stream and approaches it 

 until, at Storm King Mountain, it rises 1,200 feet immediately from 

 the stream edge. Marlboro Mountain forms an equally high wall 

 on the west bank. The average valley width of 16 miles between the 

 500-foot contours, and of 32 miles between those of 1,000 feet, is 

 constricted between these mountains, and at West Point is about % 

 of a mile wide at the lower, and 2 miles at the upper elevation. 

 Similar widths at these levels along the Rondout-Wallkill Valley are 

 •from 2 to 6 for the lower, and 16 miles for the upper one. At the 

 time of the depression of 200 feet, indicated by the above isobase, 

 the above saddle still rose 314 feet above the then ocean level, and 

 prevented a flow of water towards Delaware River, if the Storm 

 King-West Point pocket were open. 



Going north from the pocket we come suddenly, at Kingston, 

 upon thick clean, horizontally-bedded brick-clay carrying infrequent 

 good-sized boulders. Still further to the -north the clay grows thin 

 and sandy, with gradual change to foreset-bedded gravel dipping 

 down stream, and in sporadic patches where sheltered from the cur- 

 rent. The clay and boulders indicate a current of 2 inches, or less, 

 per second ; a depth of water sufficient to float icebergs so high above 

 the deposit of clay as not to disturb its quiet and even deposition ; a 



